Spokeswoman Kristen Bossi says Murphy is expected to file the required paperwork and will speak about his candidacy Thursday in his hometown of Cheshire.

Lieberman said Wednesday that he won’t seek a fifth term.

Murphy is the second Democrat to announce a run for the seat. Former Secretary of the State Susan Bysiewicz declared her candidacy Tuesday.

Democratic Congressman Joe Courtney has also expressed interest in a Senate bid. Republican Linda McMahon, who lost last November’s Senate election for Chris Dodd’s seat to Democrat Richard Blumenthal, is also considering a Senate run next year.